Re: [Qemu-devel] [PATCH] virtio-blk: Avoid zeroing every request structure

[Corentin Chary]

On Fri, May 14, 2010 at 11:52 PM, Stefan Hajnoczi
<address@hidden> wrote:
> The VirtIOBlockRequest structure is about 40 KB in size.  This patch
> avoids zeroing every request by only initializing fields that are read.
> The other fields are either written to or may not be used at all.
>
> Oprofile shows about 10% of CPU samples in memset called by
> virtio_blk_alloc_request().  The workload is
> dd if=/dev/vda of=/dev/null iflag=direct bs=8k running concurrently 4
> times.  This patch makes memset disappear to the bottom of the profile.
>

Did you try to profile using calloc in qemu_mallocz instead of malloc + memset ?

$ man calloc
calloc()  allocates memory for an array of nmemb elements of size
bytes each and returns a pointer to the allocated memory.  __The
memory is set to zero.__

-- 
Corentin Chary
http://xf.iksaif.net